1. Field of the Invention
The present invention relates to a radiographic image capturing system, and in particular, to a radiographic image capturing system that is capable of wired communication using a communication cable and wireless communication, and can carry out fluoroscopic imaging in which the capturing of radiographic images is carried out continuously at notified synchronization timings or at a predetermined frame rate.
2. Description of the Related Art
Radiation detectors such as flat panel detectors (FPDs), in which a radiation-sensitive layer is disposed on a thin film transistor (TFT) active matrix substrate and that can convert radiation directly into digital data have been put into practice in recent years. Portable radiographic image capturing devices (hereinafter also called “electronic cassettes”), that capture radiographic images expressed by irradiated radiation by using the radiation detector, are being put into practice. As compared with a radiographic image capturing device that uses a conventional X-ray film or imaging plate, a radiographic image capturing device that uses the radiation detector has the advantages that images can be confirmed immediately, and fluoroscopic imaging (video image capturing), in which the capturing of radiographic images is carried out continuously, also can be carried out. As methods of converting radiation at the radiation detector, there are an indirect conversion method that, after converting radiation into light at a scintillator, converts the light into charges at a semiconductor layer of photodiodes or the like, and a direct conversion method that converts radiation into charges at a semiconductor layer of amorphous selenium or the like, and the like. There exist various types of materials that can be used at the semiconductor layer in these respective methods.
As image capturing methods for fluoroscopic imaging, there are a method of capturing images at a predetermined frame rate while irradiating radiation continuously from a radiation source (continuous irradiation), and a method of, while irradiating radiation in the form of pulses synchronously with the frame rate (pulse irradiation), capturing images synchronously with the irradiation of the radiation. With pulse irradiation, the radiation can be irradiated for the time needed for imaging, and the amount of radiation that the patient is exposed to can be suppressed as compared with continuous irradiation, and there is therefore the advantage that the irradiated amount per unit time can be increased. However, with pulse irradiation, there is the need to synchronize the timing of irradiating the radiation from the radiation source and the timing of the image capturing at the radiation detector.
Japanese Patent Application Laid-Open (JP-A) No. 2009-136481 discloses a technique in which a switch for switching between continuous irradiation and pulse irradiation is provided. In imaging using C arm, when the C arm is rotated and positioning of the imaged region is carried out, the form of irradiation is switched to pulse irradiation by the switch. When capturing diagnostic images, the form of irradiation is switched to continuous irradiation by the switch, and image capturing is carried out.
JP-A No. 2009-186439 discloses, in a wireless X-ray fluoroscopic system that is physically divided into an exposure unit and a sensor unit, a technique of generating beacon signals at a period that is associated with the frame rate of image capturing, and wirelessly synchronizing the irradiation timing and the image capturing timing.
Electronic cassettes generally have better usability if communication thereof with a control device (known as a console) is wireless communication than wired communication using a communication cable.
For such cases, using the technology recited in JP-A No. 2009-186439 and generating a beacon signal with a period corresponding to a frame rate of image capture to synchronize irradiation timings with image capture timings has been considered.
However, if transmitting and synchronizing beacon signals by radio communication to synchronize irradiation timings with image capture timings is attempted, the synchronization is difficult because of communication delays and the like, and fluoroscopic images may not be captured reliably.
Radio communication between an electronic cassette and a control device has been described here, but the same applies in a case in which communication between a control device and a radiation irradiation device or between an electronic cassette and a radiation irradiation device is performed by radio communication and synchronization of irradiation timings with capture timings is performed by radio communication.